Biodegradable material for injection molding and articles obtained therewith

ABSTRACT

A biodegradable material containing starch, a polyvinyl alcohol-co-vinyl acetate copolymer and plasticizer is provided. The material is injection moldable to produce articles such as those for entertaining animals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Italian Application MI2006A002374,filed Dec. 12, 2006 disclosure of which is incorporated herein byreference.

The present invention relates to a starch based biodegradable materialand to articles obtained therefrom, in particular articles to entertainanimals.

More particularly, the invention refers to articles in the form of abone or other object for chewing, thus being more attractive to theanimals such as pets.

Said articles can be molded according to the injection moldingtechnique, with short molding cycles, even in the event of considerablethickness.

Moreover, said articles are digestible in conditions simulating those ofthe gastric and intestinal environment.

Starch based materials utilized to produce articles to entertain animalsare known in the literature. For example, the U.S. Pat. No. 5,419,283describes a chewable article for animals obtained from a degradablecomposition comprising a first material chosen in the group consistingof starch, hydrolyzed starch, dextrins derived from starch and mixturesthereof, and a degradable ethylene copolymer chosen in the groupconsisting of polyethylene-acrylic acid, polyethylene-vinyl-alcohol, andmixtures thereof, wherein the weight ratio between said ethylenecopolymer and said first material is in the range between 1:6 and 2:1.The copolymer present in the chewable article described in said patentnonetheless has poor properties of digestibility in the gastric andintestinal environment. In the event of accidental ingestion offragments of said article by the animal, this could therefore causeproblems linked to the poor digestibility.

Moreover, the polymer mixture described in the U.S. Pat. No. 5,419,283has low fluidity in the usual processing conditions with injectionmolding press, which causes a high consumption of energy duringprocessing with industrial processing plants.

A further disadvantage of the polymer mixture described in the aforesaidpatent lies in the fact that it has low crystallization temperatures.Short molding cycles, on industrial injection molding plants, aretherefore difficult to achieve, with evident negative effects onproduction.

The object of the present invention is to overcome said drawbacks, andin particular to provide a starch based biodegradable material suitableto be processed industrially. Said material is particularly suitable toproduce articles to entertain animals endowed with properties ofdigestibility at gastric and intestinal level. These properties would,in fact, be extremely desirable as the entertainment articles accordingto the invention are susceptible to ingestion by the animal.

A further object of the present invention is to provide a starch basedbiodegradable material with increased fluidity in injection moldingconditions and a higher crystallization temperature, thereby allowingthe industrial output to be improved.

The aforesaid objects are achieved by means of a biodegradable materialcomprising starch, a polyvinyl alcohol-co-vinyl acetate copolymer and atleast one plasticizer.

The characteristics and advantages, with respect to prior art, of thebiodegradable material according to the invention, and of the articlesobtained therewith, will be evident from the description below.

FIG. 1 shows an embodiment of the biodegradable material according tothe invention, in the form of a bone for dogs.

The biodegradable material according to the present invention comprisesstarch, a polyvinyl alcohol-co-vinyl acetate copolymer and at least oneplasticizer. The term starch is intended herein as all types of starch,namely: flour, native starch, chemically and/or physically modifiedstarch, hydrolyzed starch, destructured starch, gelatinized starch,thermoplastic starch. Particularly suitable according to the inventionare potato starch, corn starch, wheat starch, pulse, tapioca, yucca andsorghum starch. In the mixture according to the invention, the drystarch is present in an amount between 20 and 90%, preferable between 25and 80%, and even more preferably between 30 and 70% by weight withrespect to the total weight of the composition.

With regard to the polyvinyl alcohol-co-vinyl acetate copolymer, it ispresent in a quantity ranging between 5 and 50%, preferably between 10and 40% and even more preferably between 15 and 35% by weight, withrespect to the total weight of the composition.

It has a degree of hydrolysis >95%, preferably >97% and even morepreferably >99%.

The plasticizer can be any substance known to one averagely skilled inthe art for this use such as, for example, glycerol, water, sorbitol andpentaerythritol. The water can be that contained in the starch.

Particularly suitable are solid plasticizers at ambient temperature,such as sorbitol and pentaerythritol. The plasticizer is present in anamount preferably between 5 and 45%, more preferably between 10 and 43%and even more preferably between 15 and 40% by weight with respect tothe total weight of the composition.

In a particularly preferred embodiment, glycerol, water and sorbitol areadvantageously utilized as plasticizers of the starch and of thepolyvinyl alcohol-co-vinyl acetate copolymer. The biodegradable materialdescribed in the present invention has a viscosity in molten state,measured at T=180° C. and γ_(ap)=103 s⁻¹, <1200 Pa·s, preferably <800Pa·s, more preferably <600 Pa s and a crystallization temperature >105°C., preferably >110° C.

The biodegradable material according to the invention therefore has highfluidity which allows improved industrial processability and a highcrystallization temperature which brings about an increase inproductivity.

Generally, the biodegradable material according to the inventioncontains water in a range between 2.5 and 8%, preferably between 3 and6% in weight with respect to the composition.

Naturally, other substances can be added to said material, such ascolorings, flavorings, food supplements, fibers and process additivessuch as fluidifying and slip agents.

The process additives are preferably chosen in the group consisting ofcalcium stearate and zinc stearate and are present in a quantity between0.1 and 5%, preferably between 0.5 and 3% by weight with respect to thetotal weight of the composition.

The articles for entertaining animals obtained from the biodegradablematerial according to the invention have a digestibility of >80%,preferably >85%, expressed in terms of loss of weight of the sample, ina gastric and intestinal environment.

Moreover, if immersed in water at T_(amb) for 3 minutes said articlesare not slippery and do not release sticky residues.

Finally, a further advantage of the aforesaid articles is given by thefact that, when exposed for 12 hours to a T of 23° C., in low humidityconditions (50% RH or under a nitrogen flow), they maintain sufficientbreaking energy to avoid self-fracturing. This makes the use of costlyprotective packaging unnecessary.

The biodegradable material according to the invention can alsoadvantageously be used to produce, for example, thermoformed and foamedfilms and for lacquer coating and layers of multilayers with otherplastic materials, of cellulose or aluminum.

The invention will now be described by means of some embodiments,provided purely by way of example.

EXAMPLE 1

A twin screw extruder with D=30 mm, L/D=35, was supplied with:

-   -   48.8% corn starch (containing 12% water)    -   23.7% PVOH-co-vinyl acetate with degree of hydrolysis of 99%    -   10.8% glycerol    -   15.6% sorbitol    -   1.1% calcium stearate

Operating conditions of the extruder:

-   -   thermal profile: 30-90-170×7-160×4    -   flow rate: 10.1 kg/h    -   rpm=170    -   active degassing

The material delivered from the production line was cut at the headthereof to obtain granules which are air cooled.

The granules thus obtained were characterized by a water content of 4%in weight.

The granules thus obtained were subjected to rheological and thermalcharacterization tests.

Rheological Characterization

The mixture with the composition as per Example 1 was melted in acapillary rheometer mod. Goettfert (L/D=30) and the viscosity was thenmeasured (η_(ap)) at T=180° C. and γ_(ap)=103 s⁻¹. A value of η_(ap)=329Pa·s was recorded.

Thermal Characterization

DSC analysis of a mixture with a composition as per Example 1 highlightsa crystallization temperature of 120.1° C.

Subsequently, the granules obtained according to the process describedabove were fed to an injection molding press.

The operating conditions of the injection press mod. Sandretto S/7, inwhich a bone-shaped mold according to the drawing 1 is present, were asfollows:

-   -   thermal profile: 140-150-160-170° C.    -   injection speed: 40 cm³/s

The bone is molded in a 22 second cycle.

The bone thus obtained was subjected to a gastric and intestinaldigestibility test and to a soiling test.

Digestibility Test

The test was conducted according to the method of Van Der Meer andPerez. A description of the method of Van Der Meer and Perez is given inthe Journal of the Science of Food and Agriculture, 1992, vol. 59,n^(o)3, pp. 359-363.

Samples of fragments of bone according to the invention of the weight of10-20 grams were made to react in pH conditions simulating first thegastric and then the intestinal environment, consecutively.

A weight loss of the sample of >85% is recorded; the residue was softand easily digestible.

Soiling Test

Bones produced according to the invention were subjected to anexperimental test to assess their potential to soil garments or fabricsduring their use. After immersion in water for 3 min at T_(amb) it wasobserved that they were not slippery and did not release stickyresidues. Moreover, following rubbing on a black fabric cloth, it wasobserved that they left no visible solid residue but a film composedmainly of 93% water. After drying of the cloth only small traces ofsolid powder were observed.

COMPARISON EXAMPLE 1

The extruder of Example 1 was supplied with:

-   -   49.4% corn starch (containing 12% water)    -   18.3% of EVOH    -   8.5% of glycerol    -   23.4% of sorbitol    -   0.4% erucamide

Operating conditions of the extruder:

-   -   thermal profile: 30-100-170×14    -   flow rate: 10.1 kg/h    -   rpm=170    -   active degassing

The material delivered from the production line was cut at the headthereof to obtain granules which were air cooled.

The granules thus obtained were characterized by a water content of 5%in weight.

The granules thus obtained were subjected to rheological and thermalcharacterization tests.

Rheological Characterization

The mixture with a composition as per Comparison Example 1 was melted ina capillary rheometer mod. Goettfert (L/D=30) and the viscosity was thenmeasured (η_(ap)) at T=180° C. and γ_(ap)=103 s⁻¹. A value of η_(ap)=791Pa·s was recorded.

Thermal Characterization

DSC analysis of a mixture with a composition as per Comparison Example 1highlights a crystallization temperature of 96° C.

Subsequently, the granules obtained according to the composition and theprocess as per Comparison Example 1 above were fed to the injectionmolding press of Example 1 and subjected to a molding cycle in the sameoperation conditions as Example 1.

The bone is molded in a 35 second cycle.

The bone thus obtained was subjected to a gastric and intestinaldigestibility test.

Digestibility Test

The test was conducted according to the method of Van Der Meer and Perezpreviously mentioned (see Example 1).

A weight loss of the sample of <26% was recorded; the residue wasrubbery in consistency, without sharp edges.

COMPARISON EXAMPLE 2

The extruder of Example 1 was supplied with:

-   -   35.5% corn starch (containing 12% water)    -   29.7% PVOH-co-vinyl acetate with degree of hydrolysis of 88%    -   9.0% of glycerol    -   12.9% of sorbitol    -   12.9% of water

Operating conditions of the extruder:

-   -   thermal profile: 30-90-170×8-150×4    -   flow rate: 10.1 kg/h    -   rpm=170    -   active degassing

The material delivered from the production line was cut at the headthereof to obtain granules which were air cooled.

The granules thus obtained were characterized by a water content of 5%in weight.

The granules thus obtained were subjected to rheological and thermalcharacterization tests.

Rheological Characterization

The mixture with a composition as per Comparison Example 2 was melted ina capillary rheometer mod. Goettfert (L/D=30) and the viscosity was thenmeasured (η_(ap)) at T=180° C. and γ_(ap)=103 s⁻¹. (η_(ap)). A value ofη_(ap)=1229 Pa·s was recorded.

Subsequently, the granules obtained according to the composition and theprocedure as per Comparison Example 2 were fed to the injection moldingpress of Example 1 and subjected to a molding cycle in the sameoperating conditions as Example 1.

The bone was molded in a 40 second cycle.

The bone thus obtained was subjected to a soiling test.

Soiling Test

Bones produced according to the composition and the process as perComparison Example 2 were subjected to an experimental test to assesstheir potential to soil garments or fabrics during their use. Afterimmersion in water for 3 min at T_(amb) it was observed that they becomeflaky on the surface and release sticky residues.

1. Biodegradable material characterized in that it comprises: starch,present in an amount between 20 and 90% by weight with respect to thetotal weight; a polyvinyl alcohol-co-vinyl acetate copolymer present inan amount between 5 and 50% by weight with respect to the total; atleast one plasticizer, present in an amount between 5 and 45% withrespect to the total; wherein said polyvinyl alcohol-co-vinyl acetatecopolymer has a degree of hydrolysis of >95%.
 2. Biodegradable materialas claimed in claim 1, characterized in that said degree of hydrolysisis >97%.
 3. Biodegradable material as claimed in claim 1, characterizedin that said degree of hydrolysis is >99%.
 4. Biodegradable material asclaimed in claim 1, characterized in that said starch is present in anamount between 25 and 80% by weight.
 5. Biodegradable material asclaimed in claim 1, characterized in that said starch is present in anamount between 30 and 70% by weight.
 6. Biodegradable material asclaimed in claim 1, characterized in that said polyvinylalcohol-co-vinyl acetate copolymer is present in an amount between 10and 40% by weight with respect to the total weight.
 7. Biodegradablematerial as claimed in claim 1, characterized in that said polyvinylalcohol-co-vinyl acetate copolymer is present in an amount between 15and 35% by weight with respect to the total weight.
 8. Biodegradablematerial as claimed in claim 1, characterized in that said plasticizeris present in an amount between 10 and 43% by weight with respect to thetotal weight.
 9. Biodegradable material as claimed in claim 1,characterized in that said plasticizer is present in an amount between15 and 40% by weight with respect to the total weight.
 10. Biodegradablematerial as claimed in claim 1, characterized in that said starch iscorn starch.
 11. Biodegradable material as claimed in claim 1,characterized in that said plasticizer is selected from the groupconsisting of glycerol and water.
 12. Biodegradable material as claimedin claim 11, characterized in that said plasticizer is the water presentin the starch.
 13. Biodegradable material as claimed in claim 1,characterized in that said plasticizer is solid at ambient temperature.14. Biodegradable material as claimed in claim 13, characterized in thatsaid plasticizer is selected from the group consisting of sorbitol andpentaerythritol.
 15. Biodegradable material as claimed claim 1,characterized in that it has a viscosity in molten state, measured atT=180° C. and γ_(ap)=103 s⁻¹, <1200 Pa·s.
 16. Biodegradable material asclaimed claim 1, characterized in that it has a viscosity in moltenstate, measured at T=180° C. and γ_(ap)=103 s⁻¹, <800 Pa·s. 17.Biodegradable material as claimed claim 1, characterized in that it hasa viscosity in molten state, measured at T=180° C. and γ_(ap)=103 s⁻¹,<600 Pa·s.
 18. Biodegradable material as claimed in claim 1,characterized in that it has a crystallization temperature >105° C. 19.Biodegradable material as claimed in claim 1, characterized in that ithas a crystallization temperature >110° C.
 20. Biodegradable material asclaimed in claim 1, characterized by further comprising a substanceselected from the group consisting of colorings, flavorings, foodsupplements and fibers.
 21. Biodegradable material as claimed in claim1, characterized by further comprising a substance selected from thegroup consisting of process additives.
 22. Biodegradable material asclaimed in claim 21, characterized in that said process additivescomprise fluidifying and slip agents, preferably chosen in the groupconstituted by calcium stearate and zinc stearate.
 23. Biodegradablematerial as claimed in claim 21, characterized in that said processadditives are present in an amount from 0.1 to 5% by weight with respectto the total weight of the composition.
 24. Biodegradable material asclaimed in claim 21, characterized in that said process additives arepresent in an amount between 0.5 and 3% by weight with respect to thetotal weight of the composition.
 25. Article to entertain animalsobtained from biodegradable material as claimed in claim
 1. 26. Articleto entertain animals as claimed in claim 25, characterized in that ithas a digestibility >80% in terms of loss of weight, in a gastric andintestinal environment.
 27. Article to entertain animals as claimed inclaim 25, characterized in that it has a digestibility >85% in terms ofloss of weight, in a gastric and intestinal environment.
 28. Article toentertain animals as claimed in claim 25, characterized in that saidarticle is preferably in the form of a bone.
 29. Films, thermoformed andfoamed, obtained from the biodegradable material as claimed in claim 1.30. Biodegradable material as claimed in claim 1, utilizable for lacquercoating and layers of multilayers with other plastic materials, ofcellulose or aluminum.